In the manufacture of transmission media for communications purposes, for example, an elongated transmission medium is moved along a path of travel and has an insulative cover applied thereto. Typically, the cover comprises a plastic extrudate. After the application of the cover, the insulated medium is moved through a cooling device wherein a cooling medium is applied to the insulated medium to cool the material comprising the cover. Following the cooling step, cooling medium remaining on the cover is removed prior to measurements and takeup. The transmission medium may be a metallic conductor such as a copper conductor, for example. Or, the transmission medium may be an optical fiber which has been provided with one or more coating materials following draw. See for example, U.S. Pat. No. 4,474,830 which issued on Oct. 2, 1984 in the name of Carl R. Taylor.
Typically, the insulated transmission medium is moved through a device called an air wipe. In the air wipe device, jet streams of air are directed into engagement with the insulative covering material. It is commonplace for the air wipe device to comprise a tube through which the transmission medium is advanced. Air introduced into the tube travels along the tube and exits with portions of the transmission medium.
There appear to be several categories of air wipe devices in the prior art. A first type relies on a relatively expensive opening and closing mechanism to facilitate string-up. Experience has shown that these are troublesome to maintain and require excessive time to string-up.
In order to control the position of the transmission medium in the tube, it is typical to provide a contacting ceramic bearing at an entrance to the air wipe device to position the transmission medium at an entrance to the tube. One problem with the ceramic entry positioning bearing relates to irregularities in the insulation cover. Should there be any lumps, for example, in that cover, passage through the close fitting bearing may be impeded and a break in the transmission medium may occur. In a third commonly used air wipe device, spring-loaded elements are used to allow the size of the passageway opening to be changed. This arrangement does not allow the passage of lumps of plastic material at relatively high line speeds and the impact of the lumps of plastic material on portions of the air wipe device togther with friction forces may cause the filamentary material to break.
Arrangements other than those just described have been sought after. First, the prior art air wipe devices are relatively expensive and the ceramic bearing portions thereof require periodic maintenance and/or replacement. Further, for product quality reasons, it would be more desirable not to have a bearing surface contact the moving transmission medium. Clearly, what is needed is an air wipe device which accommodates such irregularities while satisfying the seemingly opposing need of centering the transmission medium during its passage through the air wipe device.
Another feature which has long been sought after is ease of string-up. In those air wipe devices which are available commercially today, it is necessary to thread the transmission medium through the bearing and the tube, or to open and close a hinged device. This is somewhat time consuming and must be done while stringing up the elongated material through other apparatus of the insulating line. What is needed is an air wipe device which is capable of relatively rapid string-up and which cannot be left ineffectively open as in the case of the hinged devices.
Efficiency of the air wipe device is another consideration. In at least some air wipe devices available commercially today, the jet streams of air, as they enter the tube through which the elongated material is being moved, are opposed to each other. As a result, some portions of the moving transmission medium are not exposed directly to an air stream emanating from a jet orifice. In other words, there are so-called dead spots on the moving elongated material, that is portions of the surface area which are not exposed to the wiping fluid. As a result, the efficiency of known prior art air wipe devices is not as high as might be expected.
What is needed and what seemingly is not provided in the prior art is an air wipe device having relatively high efficiency and being non-contacting. The sought after arrangement should be one which is low in initial cost and in maintenance. Further, it should allow the passage therethrough of any expected projection of the insulation cover material.